1. Field of the Invention
The present invention is broadly concerned with improved seal assemblies for use with elongated, axially rotatable shafts used in blenders or other mixing devices, in order to permit rapid repair of shaft seals without the need for complete breakdown of the blenders. More particularly, the invention is concerned with such seal assemblies, as well as corresponding shaft assemblies and blending devices, wherein the shaft seal assemblies include a replaceable tubular sleeve adapted to be disposed about a shaft and is rotatable therewith, in conjunction with an annular sealing body disposed about the sleeve and supporting a seal at a first sealing location. A locking device is provided for maintaining the sealing body in a shaft-sealing position, and the sleeve is selectively movable relative to the shaft so as to change the sealing location from the first to a different, second sealing location.
2. Description of the Prior Art
Food and pharmaceutical manufacturers commonly make use of large blending or mixing devices which include an upright tank as well as one or more elongated mixing shafts extending into the confines of the tank. For reasons of sanitation, such mixing shafts are typically fabricated from stainless steel material. In any case, in order to obtain the necessary, fluid-tight seal, the mixing shafts are equipped with stationary elastomeric external seals. A problem arises, however, because of the fact that stainless steel is a relatively soft material. Thus, during rotation of the mixing shafts, a groove or indentation is worn in the shaft at the region of the surrounding seals. When this occurs, the overall seal degrades and begins to leak. This necessitates essentially a complete blender teardown because of the need to replace the shaft or at least remachine the shaft. This is an expensive proposition not only from the standpoint of repair costs, but also because of blender downtime.
It has been suggested in the past to heat treat the stainless steel mixing shafts in order to extend the useful lives thereof. While such heat treating does harden the shafts, it is very expensive and thus has not been widely practiced.
There is accordingly a need in the art for an improved shaft sealing assembly which permits rapid sealed repair without the need for complete blender breakdown, while avoiding the undue expense of heat treating blender shafts.
The present invention overcomes the problems outlined above, and provides a seal assembly for an elongated, axially rotatable shaft such as those used in blender or like devices, and which efficiently solves the seal repair problem. Broadly speaking, the seal assembly of the invention includes a tubular sleeve adapted to be disposed about the shaft and is rotatable therewith, in conjunction with an annular sealing body disposed about the sleeve in a sealing position and supporting a resilient seal which engages the sleeve at a first sealing location thereon. A locking device is used to maintain the sealing body in the sealing position. In use, the sleeve is selectively movable relative to the shaft and sealing body so as to change the sealing location thereon from the first sealing location to a second, different sealing location.
In preferred forms, an interlock is provided between the sealing body and sleeve in order to selectively lock the sleeve relative to the sealing body. This interlock structure advantageously takes the form of two or more axially spaced apart grooves formed in the exterior surface of the sleeve, and a complemental locking projection or lug on the sealing body; the lug is alternately received in the grooves in order to vary the sealing location presented by the sleeve. The locking device is preferably in the form of an apertured plate engaging the exterior of the sealing body, with releasable retainers or clamping the plate against the sealing body.
In use, the sleeve is telescoped onto the mixing shaft, preferably through the use of a key/keyway interconnection, and the sealing body is positioned about the sleeve so that a seal carried by the body engages the sleeve at a first location. The locking device is then attached to complete the assembly. As the shaft rotates and a groove or indentation is formed in the sleeve, a leak may develop. When this occurs, it is only necessary to disassemble the seal assembly and shift the sleeve to present a second, different sealing location for the sealing body upon reassembly.
The invention also permits complete removal and replacement of the tubular sleeve, thereby even further extending shaft life. Finally, inasmuch as the replaceable sleeve is a relatively small, usually stainless steel component, heat treatment of the sleeve is economically justifiable.